1. Field of the Invention
The present invention relates to a thermally resistant resin composition containing polystyrenes (PS) and polyphenylene oxides (PPO).
2. Prior Art
Resin compositions produced by blending PS with a glass transition point (Tg) of about 100.degree. C. and PPO with Tg of about 210.degree. C. together, have been known widely as one class of thermally resistant polymer alloys in a uniformly miscible system. The PS/PPO resin compositions have single Tg approximately corresponding to the arithmetic mean of the Tgs of the two polymers.
Because PS/PPO resin compositions show excellent electric performance such as dimensional stability, mechanical properties, insulating properties and high-frequency performance, furthermore, the compositions are utilized in resin molded articles such as housings of electric appliances and electronic devices including television sets, air conditioning systems, computer systems; chassis for office appliances for example copying machine and facsimile; various containers (trays and the like); and automobile parts such as instrument panel.
Such PS/PPO resin compositions do not generate hazardous substances such as corrosive gases and dioxin during combustion because the compositions do not contain halogen atoms. In that sense, the compositions are fairly safe. Additionally because PS/PPO resin compositions have excellent thermoplasticity, the compositions can be melt again after the molding process to be put to re-molding process. Thus, PS/PPO resin compositions are considered as recyclable resources. Hence, the utility (applicable range) of PS/PPO resin compositions has been expected to be enlarged from the enhanced need in recent years to preserve the global environment.
The field of the materials for printed board requiring soldering heat resistance (180.degree. C.) is included in one of their applicable range to be enlarged.
Conventional materials for printed board include for example a composite material such as glass epoxy resin-immersed paper and phenol resin-immersed paper, but it is difficult to separate the individual materials constituting these composite materials. Furthermore, the resins used therein are thermosetting. Therefore, these materials are disadvantageous in that reprocessing (recycling) of these materials via melting is substantially impossible while PS/PPO resin compositions can be recycled. Accordingly, it has been desired to use recyclable PS/PPO resin compositions as printed board materials instead of conventional materials for printed board.
However, the glass transition point of conventional PS/PPO resin compositions corresponds to the arithmetic mean of the Tgs of the two polymers, so that a higher content of PS causes lower Tg compared with the Tg of a resin of 100% PPO. Thus, the heat resistance of PS/PPO resin compositions is poorer than that of the resin of PPO alone.
So as to improve the heat resistance of PS/PPO resin compositions, alternatively, it is proposed to improve the glass transition point of the compositions by introducing a sulfonic acid group into either one or both of PS and PPO and reacting sodium methoxide with the sulfone group to form an ionic bond between the polymer chains (Don-Tsai Hseih et al., Polymer, Vol.33, No. 6, 1210 (1992)).